DEMIXING VS FREEZING OF BINARY HARD-SPHERE MIXTURES

The absence of demixing in the Percus-Yevick theory of fluid mixtures of additive hard-spheres is related to the fact that this theory predi cts incorrect virial coefficients B-n for n >3. Incorporation of the e xact B-n for 1 less than or equal to n less than or equal to 5 into a rescaled virial expansion is shown instead to lead to demixing for any size asymmetry between the spheres. This demixing is however thermody namically metastable relative to freezing of the mixture into a partia lly ordered solid phase. This conclusion is reached on the basis of a density functional estimate of the free-energy of a nonuniform phase i n which the large spheres form a face-centered cubic lattice whereas t he small spheres remain disordered. (C) 1998 American Institute of Phy sics. [S0021-9606(98)51338-4].